implemented chat archive

app/lib/features/chat_archive/utils/markdown_to_text.dart

@@ -0,0 +1,9 @@
+import 'package:html/parser.dart' as html_parser;
+import 'package:markdown/markdown.dart' as md;
+
+String markdownToText(String markdown) {
+  final html = md.markdownToHtml(markdown);
+  final document = html_parser.parse(html);
+
+  return document.body?.text ?? '';
+}